We propose to assess the effects of alterations in the dietary regimen of apparently healthy human subjects on plasma concentration, composition and metabolism of high density lipoproteins (HDL) and other lipoproteins. Dietary variables will be degree of polyunsaturation of dietary fat and dietary cholesterol intake. Calorie restriction and exercise as means of achieving weight reduction in obese young women will be included as further variables. The design of the proposed experiment will lend itself to evaluation of effects of individual nutrients--fat or cholesterol--or their interactions on HDL and other lipoproteins. The mechanism of the interrelationship of HDL with recognized risk factors of cardiovascular diseases (CVD) is not yet understood. Data relating effects of the dietary variables as described on HDL and HDL subfractions could contribute to the elucidation of the interactions of HDL and risk factors of CVD. Specifically, it is proposed to quantitate and characterize HDL and other lipoproteins by lipid analysis and by quantitation of apoproteins using immunoassays or polyacrylamide gel electrophoresis-gel scanning technique. HDL subfractions will be isolated and subjected to similar analysis. In addition it is hoped to contribute to an understanding of the functional mechanism of HDL and HDL subfractons relating to any protective role that these lipoproteins may have. Both in vivo and in vitro determinations of LCAT activity are planned. The enzyme will be assayed in plasma obtained from subjects on the various dietary regimens as well as in an artificial liposome containing HDL subfractions in the presence of purified LCT. The LCAT activity in the plasma and in the artificial liposome will be related to apoprotein concentrations or ratios. This analysis could help to identify a specific HDL subfraction or component which may be related to recognized risk factors of CVD.